Electromagnetic forming coil

ABSTRACT

MAGNETIC PULSE FORMING APPARATUS INCLUDES AN ELECTROMAGNETIC FORMING COIL WITH MEANS FOR CONNECTION TO A PULSE-SOURCE OF ELECTRICAL ENERGY, SEPARABLE PORTIONS HAVING AN OPEN AND CLOSED POSITION, AND A CONTACTOR FOR PROVIDING APLURALITY OF PARALLEL CURRENT PATHS OF SUBSTANTIALLY EQUAL INDUCTANCE ACROSS NON-INTERFACING SURFACES OF THE SEPARABLE COIL PORTIONS TO PRODUCE EQUAL CONPOSITION. MEANS ARE ALSO PROVIDED TO PRODUCE EQUAL CONTACT RESISTANCE AT ALL CONTACT POINTS TO THE CONTACTOR SO THAT. OVERALL, A UNIFORM CURRENT DISTRIBUTION IS PRODUCED OVER THE PLURALITY OF PATHS WHEN THE COIL IS PULSED.

Oct. 5, 19.71

Filed June 30, 1969 P. WILDl 3,610,007

ELECTROMAGNETIC FORMING COIL 4 Sheets-Sheet 1 ACTUATOR 38 an 26d PULSEcunaem scum:

FIGJ FIG. 5 H62 as ao-- S? Q? ACTUATOR 1 INVENTOR FIGA P404 Maw ATTY5.

Oct. 5, 1971 P. WILD! 3,610,007

ELECTROMAGNETIC FORMING COIL Filed June 30, 1969 4 Sheets-Sheet 5;

FIG.6

I N VE N TOP 9401 M407 MM, M4 904, @4, 72m

ATT'YS.

Oct. 5, 1971 P. WILD] 3,610,007

ELECTROMAGNETIC FORMING COIL Filed June 30, 1969 4 Sheets-Sheet 3 9F|G.8 FIG .9 T 44 44 mvzm'oz PAM. Mzp/ Oct. 5, 1971 P. WlLDI 3,610,007

ELECTROMAGNETIC FORMING COIL Filed June 30, 1969 4 Sheets-Sheet 4 UnitedStates Patent 01 iice Patented Oct. 5, 1971 3,610,007 ELECTROMAGNETICFORMING COIL Paul Wildi, San Diego, Calif., assignor to Gulf GeneralAtomic Incorporated, San Diego, Calif. Filed June 30, 1969, Ser. No.837,464 Int. Cl. B2ld 26/14 US. C]. 72-56 14 Claims ABSTRACT OF THEDISCLOSURE Magnetic pulse forming apparatus includes an electromagneticforming coil with means for connection to a pulse-source of electricalenergy, separable portions having an open and closed position, and acontactor for providing a plurality of parallel current paths ofsubstantially equal inductance across non-interfacing surfaces of theseparable coil portions when in the closed position. Means are alsoprovided to produce equal contact resistance at all contact points ofthe contactor so that, overall, a uniform current distribution isproduced over the plurality of paths when the coil is pulsed.

The present invention relates generally to forming apparatus, and moreparticularly to apparatus for forming a workpiece by energy acquiredfrom a varying magnetic field.

Various apparatus have heretofore been developed for forming materialsby employing a varying magnetic field of high intensity. In suchapparatus generally, an electrical current pulse of high amperage andshort duration is passed through a conductor, typically in the form of acoil, to thereby produce a pulsed magnetic field of high intensity inthe proximity of the workpiece positioned in or adjacent the coil. Theworkpiece, which is typically of a conductive material or employedtogether with a conductive material, is positioned in the pulsedmagnetic field and a current pulse is thereby induced in the work piece.This current pulse then interacts with the varying magnetic field toproduce a force acting on the workpiece. The resulting force, ormagnetic pressure, is made sufficiently great to cause the desireddeformation of the workpiece, the swaging of one piece to another, etc.Repeated pulses of current may be applied to the conductor or coil, thuscausing a series of deforming impulses to be applied to the workpiece.

As indicated above, such apparatus for electromagnetic forming of aworkpiece may typically employ a conductor in the form of a coil,generally termed a work coil, forming coil, or shaper, which surroundsthat part of the workpiece to be formed so that radially directed forceswill be applied to the workpiece. For example, in the typical case ofmagnetic swaging, it is generally possible to insert an elongateduniform workpiece into the forming coil aperture or opening whichdefines the coil workspace. However, when using such a forming coil withcertain types or shapes of workpieces, a problem may arise in that theworkpiece cannot be inserted within the coil aperture, or the formedassembly cannot be withdrawn from the aperture. This problem may arise,for example, in connection with workpieces having a generally dumbbellshape, wherein the end portions may be flanged or otherwise dimensionedso as to be larger than the coil aperture, making it impossible to passthe workpiece therethrough. The coil aperture must be sufficiently smallat the working area to provide sufficient pressure for an eificientforming operation. Further, other applications and workpiececonfigurations may also prevent the workpiece from being insertedaxially into the forming coil, and examples of such configurations arethose which are closed in themselves, such as a ring, or those which,for some other reason, cannot be threaded through the coil. Examples ofthis latter type are swaging applications on pipelines or electricalconductors which, by reason of their indefinite or long lengths, ortheir installations, cannot be threaded through a C01 Electromagneticwork coils have heretofore been proposed that could be opened, at leaston one point of their circumference, so as to be capable of gripping orextending around a workpiece. However, since the discharge current pathhas to be linked with the workpiece, such a coil structure necessarilyrequires that the current path be opened every time the workpiece isinserted or taken out of the coil aperture or workspace. Therefore, atleast one electrical contact assembly need be provided on the coilcapable of carrying the required high current pulses across theseparable coil parts and the coil must be capable of being readilyopened for insertion and removal of the workpiece. In such priorconstructions, the contacts were disposed in the interface between theseparable coil-halves, and in one particular prior construction thecontacts were formed by mating cylindrical surfaces in the coilinterface. However, with such structures the recoil or reaction of theforming coil to the magnetic pressure generated during a pulsingoperation tends to push the coil-halves apart which thus tends to lessenthe contact pressure. This tends to cause arcing, and in a relativelyshort time, the contacts may be pitted or otherwise degradedsufiiciently to impair the operation of the coil, providing only arelatively short useful coil life. Such contact failure has generallybeen the principal limitinlg factor with respect to the useful life ofsuch forming CO1 s.

Additionally, in order to provide the necessary high magnetic pressurein the workspace while at the same time providing a minimum currentdensity through the contacts, such prior proposed coil structures havegenerally required a relatively narrow width in the region of theworkspace, i.e., in the working orifice or shaper portion, of the coiland a large width in the general region of the contacts to minimize thecurrent density. For example, the cross-sectional width of the coilmight diverge from the workspace to the contact area so that the widthof the contact area would be at least four or more times as wide as theworking area. Thus, if such a design were to be extended to higherpowers, the contacting areas would have to be made wider and wider and,since the mass of the coil progresses roughly with the cube of thelinear dimensions, this requirement would very rapidly lead toundesirably heavy coils for which there is considerable difficulty inobtaining a sound piece of metal by casting or forging.

Accordingly, it is an object of the present invention to provide animproved separable or openable electromagnetic forming coil.

It is another object of the invention to provide such a forming coil inwhich the recoil of the shaper does not significantly reduce the contactpressure maintaining the closed circuit path of the coi It is a furtherobject of the invention to provide a contact system for anelectromagnetic forming coil which produces a uniform currentdistribution through the contacts to minimize degradation thereof sothat a substantially longer useful coil life is provided as compared tothe aforementioned prior structures.

It is still a further object of the invention to provide a forming coilwhich requires an actuating or latching mechanism for the coil-halveswhich need provide only a relatively small force against recoil ascompared to that required by such prior proposed designs where thelatching mechanism Was also required to maintain high contact pressure.

These and other objects of the present invention will become apparent byreference to the following description and accompanying drawings, inwhich:

FIG. 1 is a schematic elevational view of a forming coil assembly inaccordance with one embodiment of the present invention;

FIG. 2 is a partial right side view of the coil assembly of FIG. 1;

FIG. 3 is a perspective view of one of the movable contactors in theassembly of FIG. 1;

FIG. 4 is an enlarged detail view, partially in section and partially inblock, taken along line 44 in FIG. 1;

FIG. 5 is an enlarged diagrammatic representation of the contact systemof the coil assembly illustrated in FIG. 1;

FIG. 6 is an enlarged diagrammatic representation of an alternativecontact system to that shown in FIG. 5;

FIG. 7 is a partial sectional view taken along the line 7-7 in FIG. 6;

FIG. 8 is an elevation view diagrammatically showing a modification ofthe contactor of FIG. 3;

FIG. 9 is a sectional view taken along line 99 in FIG. 8;

FIG. 10 is a plan view diagrammatically showing another modification ofthe contactor of FIG. 3;

FIG. 11 is a right end view of the contact arrangement illustrated inFIG. 10; and

FIG. 12 is a view, partially in elevation and partially schematic,showing an electromagnetic forming coil system in accordance with afurther embodiment of the invention.

Referring now generally to FIG. 1, there is schematically shown anelectromagnetic single turn forming coil 10 comprising a pair ofseparable conductive members, shapers, or dies 12 and 14 having an openposition, illustrated in broken line, for insertion and removal of theworkpiece 13, and a closed position, shown in solid line, for defining aworkspace 16 containing the workpiece during the forming operation. Theworkpiece is shown for example as a shaft having a collar thereon to beswaged thereto. The conductive members 12 and 14 have opposing orinterfacing pairs of surfaces 1820 and 22-24 on opposite lateral sidesof the workspace 16 which are disposed generally normal to the plane ofmotion of the dies to define, generally, the planes of separationthereof. A layer of insulation, or an insulating air gap, is providedbetween the respective pairs of interfacing surfaces on both sides ofthe workspace 16 so that desirably no current flow is permitted throughthe interfacing surfaces from one shaper die to the other. However,current flow may be conducted between the dies 12 and 14 by contactingmeans, illustrated as movable bridging switches or contactors 26a, 26b,26c and 26d (the latter two not being visible in FIG. 1 because of theirlocation behind the coil). These contactors electrically interconnectboth of the dies or coilhalves by direct contact with respect tostationary contact pairs 28a-28a', 28b-28b', 280-280 and 28d-28d'located, generally, in planes transverse to the interfacing surfaces ofthe dies on the lateral, mutually parallel, front and back externalfaces thereof. That is, each of the stationary contacts, represented bydotted lines in FIG. 1, is on an external face or surface which is in aplane parallel to the plane in which the coil-halves are openable.Consequently, the contacting and bridging arrangement between the diesis such as to provide a sliding, rather than a separating, action in theevent of relative movement between the coilhalves, such as on recoilduring a forming operation.

The stationary contact pairs 28a and 28a, 28b and 28b, etc.,corresponding to each of the contactors 2611 through 26d, are preferablytapered with respect to each other so that they are substantially closerto each other (and to their associated interfacing surface) at theirfurthest distance from the workpiece 16 and diverge away from each other(and from the interfacing surface) at distances closer to the workspace.With such a general configuration, as Will be explained in detailhereinafter, a plurality of conductive paths may be provided by the con-4 tactors which bridge each of the interfacing portions of the dies in amanner providing substantially equal inductance as well as equalresistance in each path for uniform current flow through the contactors26a through 26d, yielding an increased contact life and, consequently, asubstantially long useful coil life.

A pulse current source, illustrated as a block 30 applies the requiredenergy to the forming coil 10 by current conduction through the dies 12and 14. In the embodiment of FIG. 1, the upper die 12 is movable andformed from a continuous conductive plate, while the lower die isstationary and formed from two discrete conductive plate sections 32 and34 which are separated by an insulating layer 36 so that each sectionmay be connected to an opposite pole of the source. The separableforming coil 10, which may be sometimes termed a clam-shell coil, isshown in dotted line as being openable vertically by means of theactuator 38, which may be in the form of any suitable mechanism, such asa hydraulic piston and cylinder arrangement, which lifts the upper dieto the position designated as 12'. Alternatively, the forming coil maybe opened in other manners, if desired, as will be later described inconnection with the coil assembly of FIG. 12.

More particularly, the contacts 28a through 28d and 28a through 28d maybe formed, for example, by silver strips brazed onto the planar surfacesof the dies. The contactors 26a through 26d comprise movable switchcontact assemblies which are urged against each pair or set of contactstrips to electrically and mechanically bridge the interfacing surfacesof the dies, as shown in FIG. 2, with the applied forces being indicatedby arrows 40 and 42. Consequently, with the dies 12 and 14 in theirclosed position and with the movable contact assemblies 26a through 26din their engaged position, a complete single turn coil is formed whichmay be energized by the pulse current source 30 to produce a currentflow through the coil as indicated by the arrows in FIG. 1.

Each of the movable contact assemblies 26a through 26d preferablycomprise a plurality of laminar contact blades 44, as shown in FIG. 3.These blades are retained in a holder or housing and supportingstructure 46 by means of tab portions 48 (FIG. 4) on the inner ends ofeach contact blade which are then urged outwardly by a pressure elementsuch as an elastomeric cushion 54 or the like disposed between the inneredges of the blades 44 and the back wall of the housing 46. The tabs 48are thus normally urged against the inner surfaces of the holder flanges56, but when the contactor is moved into engagement with the associatedpair of contact strips 2828' by the application of forces 40 and 42(FIG. 2), the applied force from the rod or shaft 58 is distributed bythe rigid back wall of the holder 46 and the cushion 54 to thereby applya uniform pressure to all of the contact blades 44. The contact blades44 thus provide a multitude of parallel bridging paths across thecontact strips at pairs of contact points on the forward edge of eachblade. Because the engagement pressure is uniform, an equal contactresistance is produced at each contact point.

This arrangement is shown in greater detail in FIG. 4 for the contactor2611, the other contactors having the same type of construction. Theplurality of contact blades 44 are formed from relatively thin metalstock, arranged in an adjacent and laminar manner, and are eachgenerally T-shaped, having an inner portion disposed within the cavityof the housing or holder 46 and an outer portion protruding therefrom.Each of the contact blades are movable relative to each other and to theholder 46, and each presents an outer edge which forms the contactpoints with the contact strips 28a and 28a fixed to the dies. The backwall portion of the holder 46 functions as a means for distributing theforce applied thereto by an actuator via the reciprocally movable rod orshaft 58. The distributed force is applied to the back edges of theinner portion of each of the contact blades 44 by the cushion 54interposed and confined between the back edges of the contact blades andthe wall of the holder so that a substantially high force is applied tosubstantially all of the cushion area in the direction producing contactengagement. This causes a hydrostatic-like pressure to be applied on theplurality of contact blades, resulting in a uniform pressure beingapplied thereto so that an equal contact resistance will be produced ateach of the contact points between the blades and the contact strips.Since each contact blade is independently movable with respect to theothers, and since the pressure is everywhere sub stantially equal,equalization of contact resistance occurs generally regardless of thestate of wear of the contacts. Each of the contactors may, for example,have a construction like those disclosed in copending application Ser.No. 712,777, now Pat. No. 3,487,456, filed Mar. 13, 1968, of the sameinventor, and assigned to the assignee hereof.

A supporting structure 62 comprising suitable bearing elements for themovable shaft 58 and associated parts rigidly holds this movable contactassembly in fixed relation to the forming coil. The supporting structure62 may be attached by any suitable means to a supporting frame (notshown). Thus, with the contact assemblies disposed on the externalsurfaces of the dies, any recoil of the dies during a pulse formingoperation merely results in a sliding action of the contacts, while eachcontactor provides a multitude of alternate conductive bridging pathshaving equal contact resistance at each point of contact. The contactresistance at each point of contact between a contact blade and acontact strip is maintained uniform by the hydrostatic orquasi-hydrostatic forceproducing element 54 in each of the contactors,and these elements may comprise the elastomeric cushion, previouslymentioned, or a noncompressible fluid-filled flexible container orchamber. Various exemplary structures to produce such uniform contactpressure and an equalized contact resistance are disclosed in theaforementioned copending application; however, other types of structuresmay be employed in accordance with the principles of the presentinvention, but generally less advantageously. In the contactorillustrated in FIG. 4, the cushion 54 may be composed of a rectangularlysolid elastomeric material such as rubber or rubber-like plastic whichacts similarly to a fluid in producing a hydrostatic-like orquasi-hydrostatic pressure distribution when it, itself, is laced undera high pressure or compressive force. The elastomeric material shouldgenerally be as soft as possible to yield the best hydrostaticproperties. If desired, a multiple layer cushion structure may beemployed wherein the layers vary in hardness with the harder layerdisposed adjacent the blades to prevent extrusion upon compression bythe holder which confines the cushion on its other five sides.

Now, in accordance with a further feature of the present invention toprovide a uniform current distribution through the alternate parallelcurrent paths of each contact arrangement, because of the inherentnon-uniform current density in the coil, the contact arrangement isconfigured and arranged so as to provide substantially equal inductanceand resistance over each of these parallel paths. Thus, with equalcontact resistance at each contact point and with equal resistance andinductance over each current path, a substantially uniform currentdistribution is provided over the entire contact area of each contactorwhen the coil is pulsed to further increase the contact life and theuesful life of the coil assembly.

More particularly, the inductance of the current paths through each ofthe contactors is equalized by varying the length of each successivecurrent path a suitable amount for the particular geometry involved soas to compensate for the particular uneven current distribution in theforming coil. Referring again to FIG. 1, and as previously mentioned,the lower die 14 comprises the two conductive sections 32 and 34 whichare electrically insulated from each other by the insulation 36, andeach section is coupled to a respective pole or terminal of the source30. The workspace 16 is defined generally in the central region of theforming coil by an aperture formed by the interior curved surfaceportions 82, 84 and 86, of each of the respective coil parts 12, 32 and34. Thus, for example, the current path may be from the source 30, tothe stationary part 32, through contactors 26a and 260, movable die 12,contactors 26b and 26d, stationary die section 34 and back to the source30. However, because of the high-frequency components of currentproduced by the pulse current source 30 when discharged through theforming coil 10, a non-uniform current distribution is produced therein.More specifically, the current may be considered as travelingessentially adjacent to and on opposite sides of the insulation 36, andin the area adjacent the coil aperture or workspace 16, opposite theworkpiece placed therein, as indicated by the path of the arrows shownin FIG. 1. These are actually the high current density regions of thecoil with the current density decreasing as a function of distance awayfrom these regions during each current pulse.

A fragmentary view of the forming coil is presented in FIG. 5 showing anenlarged and very diagrammatic repthe contact strips 28a and 28a forfacilitating an understanding of the principles of this aspect of theinvention. The contact blades of contactor 26a are represented forsimplicity by the parallel sequence of five spaced vertical conductorelements 44a through Me which are representative of the edges of thecontact blades 44 illustrated in FIG. 3, but actually assembled in anadjacent laminar manner. Since the current flowing through thestationary die section 32 is concentrated near or adjacent to theinsulation 36 and tends to flow adjacent the workspace aperture 16, thecurrent is believed to take different and alternate paths, as indicatedby the arrows, through each of the conductor blades 44a through 44:: tothe movable die 12 in which the current continues to follow the pathadjacent the workspace aperture 16. The conductor blades 44a through 44cmake contact with portions of contact strips 28a and 28a, and the pointsof contact are thus made at positions 60 and 62, 64 and 66, 68 and 70,72 and 74, and 76 and 7-8. The contact resistance at each contact pointis made equal in the manner previously discussed. In addition, however,the contact strips 28a and 28a (and their respective counterparts) aredisposed so as to be diverging toward the coil aperture or workspace 16so that the edges of the blades 44a, 44b, etc., between respectivecontact points 60 and 62, 64 and 66, etc., vary in elfective electricallength to produce an equal inductance in each of the parallel paths.More particularly, in view of the current distribution of FIG. 5, thecurrent can take alternate paths through the different contact blades.If the contact strips 28a and 28a were parallel, i.e., at right anglesto the blades, so that the contact points were at equal distances fromthe interfacing surfaces 22 and 24, the various current paths would beof substantially diiferent lengths. Since the effective inductance ofeach path is generally proportional to its effective length and thereactance is generally proportional to its inductance, a very unevencurrent distribution may result through the contactors. Anotherimpairing factor, although believed to be less significant than theinductance, is the varying resistance over each of the current paths dueto their different lengths (i.e., the different distances the currentmust travel), even assuming equalized contact resistance. Consequently,in operation, the limit of current carrying ability for the bladescloser to the workspace would likely be reached long before the limitfor blades further away. However, by varying the spacings of the contactpoints in a diverging manner, the effective lengths of the current pathsare increased as a function of distance toward the workspace, thusincreasing the inductance and, to some extent, the resistance of eachsuccessive path to compensate for the different path lengths through thecoil. Therefore, it is generally advantageous to bring the points 60 and62, i.e., those furthest from the workspace, as close to the interfacegap as possible so as to minimize the inductance ofi the furthest path.Then the current paths closer to the workspace are brought up to thesame value of inductance by spreading the successive pairs of points 64and 66, 68 and 70, 72 and 74, and 76 and T8 successively wider apart.Although the drawing of FIG. shows the strips 28a and 28a (as well astheir counterparts) as straight or nearly straight lines, thisorientation will generally represent merely an approximation of theoptimum shape or configuration. The particular shape, which may be acurve, to produce the desired or optimum variations in length of thebridging between contact points of each successive conductor blade maybe established from a magnetic field plot for any particular coilgeometry.

Referring now to FIGS. 6 and 7, there is shown an alternative form ofstationary contact structure 100 and 102 associated respectively witheach die or coil-half 12 and 14. The contactor 26a is structured aspreviously described in connection with FIGS. 3 and 4. However, insteadof employing contact strips such as 28a, 28a, etc., shallow depressions104 and 106 are milled into the surface of each of the dies and thelengths of the current paths corresponding to each of the contactorblades is then accomplished by suitably shaping the edges 108 and 110 toprovide the equalized inductance (and path resistance) previouslydescribed. The eifective lengths of the current paths through thesuccessive contactor blades thus correspond to the varying distancebetween the milled edges 108 and 110 across which the contact bladesbridge one shaper to the other. The application of a substan tially highforce on the contactor 26a is represented by the arrow 112 in FIG. 7 ina manner similar to that of FIG. 2.

The same general results with respect to equalizing the path inductanceand resistance may alternatively be achieved by varying the effectivepath lengths by particularly shaping the contactor blades rather thanthe stationary contact sets. Referring now to FIGS. 8 and 9, there isshown a modified form of the contact blades 44 of the contactorillustrated in FIG. 3. In the modified form, the contactor blades 44'are generally recessed with two raised projections or protrudingportions on each blade arranged in such a manner as to form the desiredcontact configuration for equalization of path inductance and resistancewhen mating with parallel contacts on the dies, i.e., contacts which areequally and uniformly spaced from the interface gaps of the coil. Thespacing between the projecting portions 114 and 116, as shown in PEG. 9,on each successive blade is determined in the same manner as thegeometry of the fixed contact strips previously described in connectionwith the embodiment of FIG. 1, the straight-line configurationsillustrated in PEG. 8 being generally an approximation to the mostoptimum geometry which may generally be a curve. As before, the mostoptimum configuration may be determined by a magnetic field plot for anyparticular coil construction, and a straight-line approximation may beemployed when balanced against other considerations such as cost andease of manufacture.

Another manner of achieving the desired equalization of inductance andpath resistance for uniform current distribution throughout the contactarea is illustrated in FIGS. 10 and 11. As there shown, the contactblades 44" are similar to those of the contactor illustrated in FIG. 3but have a channel or slot 120 of varying depth through the face of thecontact blades so that the effective length normal to the plane of thecoil 10 is varied to equalize the .inductance of each current paththrough the contactor blades. This form of contactor may be employedwith parallel stationary contacts of the same type as described inconnection with the embodiment of FIGS. 8 and 9. As shown in FIG. 11,the contact blades 44" make contact with the stationary contact strips28 and 28 on the dies 12 and 14 at the projecting edges 122 and 124, andeach successive lamination or blade provides a generally U- shapedcurrent path of successively varying length bridging the dies. As shownin FIG. 10, the added inductance for equalization is the greatest towardthe right-hand side of the figure and is the least toward the left-handside of the figure. Thus the workspace would be located to the right ofthe contact assembly as shown.

Other forms of contact arrangement may alternatively be employed inaccordance with the principles of the invention, such as, for example,an arrangement utilizing a combination of the features of theembodiments of FIGS. 1, 6, 8 and 10.

Referring now to FIG. 12, there is shown an alternative embodiment of acoil assembly to that of FIG. 1 wherein corresponding parts aredesignated with primed reference numerals corresponding to those used inFIG. 1. As in the embodiment of FIG. 1, there is a movable die 12' and astationary die 14', the latter of which is divided into two conductivesections 32' and 34 separated by insulation 36'. Each one of thecondutcive sections 32' and 34' is connected to one pole of the currentsource 30 which is merely illustrated as the housing containing amatching transformer for matching the impedance of the forming coil 10to the output impedance of the pulse power supply, the power supply andmatching transformer, per se, forming no part of the present invention.The dies are also mechanically mounted on the source housing 30', asshown. Each of the dies 12 and 14' contain pairs of contact strips ofthe type illustrated in FIGS. 1 and 2 and which diverge toward theworkspace-defining aperture 16'. Four contactor assemblies like thatdisclosed in FIGS. 3 and 4 and previously described are utilized withthe forming coil of FIG. 12, but only contactor 26b is shown for clarityof illustration.

The movable shaper or coil-half 12' is hinged for pivotal movement abouta pivot 200 and is operated by a pneumatic cylinder assembly 202 througha suitable linkage. The coil 10" is illustrated in 'FIG. 12 in its openposition for insert-ion or removal of a workpiece (not shown). Thepneumatic cylinder 202 operates the movable die 12 through a piston-rod204 pivotably attached to one end of a bell crank 206 having itsintermediate point pivotably connected to the upper die pivot hinge 200.The other end of the bell crank is fixedly attached to the upper surfaceportion of the die 12 by means of a resilient mount 208 for isolation ofshocks during the forming operation from the cylinder and linkages. Thelower end of the hydraulic cylinder assembly 202 is pivotably attachedto a mounting lug at pivot 210, the mounting lug being rigidly at tachedto the housing 30'.

Hydraulic rams are provided as the actuators (FIG. 4) associated witheach of the four contactors, but only one is schematically illustratedas 80' in FIG. 12. A hydraulic control system 212, of any suitable type,is provided as illustrated in block form and is responsive to an inputcontrol signal, indicated by arrow 214, to operate a pneumatic cylindercircuit so that the proper sequence of operations will be performed inboth opening and closing of the coil-halves. More particularly, thehydraulic rams for pressurizing the contactors may be operated by apneumatic-hydraulic booster similar to the master cylinder of anautomotive braking system which is tied into the pneumatic cylindercircuit for control by the system 212.

In operation, on actuation by the command signal on input 214, thepneumatic control circuit causes the pneumatic cylinder assembly 202 tomove the upper die 12 to its closed position to perform a formingoperation. Subsequently, in response to an appropriate signal thepneumatic-hydraulic booster causes all of the contactors to move intotheir engaged contacting position and it continues to maintain asubstantially high force on all of the contactors to provide minimum andequalized contact resistance across all of the contact points associatedwith 9. each contactor. After a forming operation has been completed,the sequence of operations is effected in reverse of that previouslydescribed so that the booster releases and withdraws each of thecontactors from their engaged position and subsequently the pneumaticcylinder assembly 202 opens the coil-halves. Of course, any other systemmay be utilized to operate the coil assembly and the contact assembliesassociated therewith, and other particular arrangements for opening thecoilhalves may alternatively be employed.

In the construction illustrated in FIG. 12, side plates 216 are boltedon both sides of the stationary die 14 so as to bridge the two sections32' and 34 of opposite polarity and these function to increase theeffective reluctance of the insulating slot or layers 36'. These sideplates may contain a conductive metallic insert or are themselves madeout of metal with suitable insulation to prevent shortening the coil.Although no insulation is shown covering the movable shaper and thestationary coil parts, such insulation may be provided if desired.Additionally, any form of suitable cooling mechanism may be provided inconjunction with the coil, if desired.

As can now be seen, the embodiments of the invention herein describedinclude contacts which are at generally right angles to the maindirection of recoil during a pulsing operation so that they will, underthe most severe conditions, experience at most only a sliding motionover their surfaces, rather than any tendency to separate which wouldlessen the contact pressure. The forces tending to repel the contactblades from such shapers is, due to the lower current density, of aconsiderably lower order of magnitude and will in the present designs beovercome by the force of the contact-actuating mechanisms described.Furthermore, since the shaper-actuating mechanism does not have toprovide contact pressure, as would be the case where the contacts werelocated in the interfacing surfaces of the dies, it can be constructedto provide a relatively smaller force. Thus, the shaperactuatingmechanism will bring the coil-halves together while the mechanism whichprovides the contact clamping force is de-energized, and only after thecoil-halves have been brought into operating relation will the contactsbe pressurized into contacting engagement.

A further advantage of the present designs is that they permit the useof rolled or forged materials in plate form which is readily available;and in addition, the contacts can be made relatively small and are solocated that they will, in general, not interfere with either theworkpiece itself or the positioning mechanisms which may typically beutilized with such a forming coil.

Various modifications of the features and embodiments disclosed hereinwill be apparent to those skilled in the art; and as such, the scope ofthe invention should be defined only by the claims, and equivalentsthereof.

Various features of the invention are set forth in the following claims.

What is claimed is:

1. Apparatus for electromagnetically forming a workpiece, comprising apair of relatively separable conductive members having an open positionfor insertion and removal of the workpiece and a closed positiondefining a workspace for the forming operation, means for coupling saidconductive members to a pulse-source of electrical energy to cause anelectrical current to flow through said conductive members, saidconductive members having a predetermined path of relative movementbetween said open and closed positions and respective insulativelyspaced interfacing surfaces generally transverse to said path ofrelative movement, said conductive members having respective contactsurfaces adjacent said interfacing surfaces and disposed generallyparallel tosaid path of movement of the conductive members, andcontacting means electrically interconnecting both of said conductivemembers by contact therewith at said respective contact surfaces so asto bridge the interfacing surfaces when said conductive members are insaid closed position.

2. The apparatus of claim 1 wherein said contacting means includes meansfor providing a plurality of conductive parallel bridging paths acrosssaid contact surfaces of said separable conductive members.

3. The apparatus of claim 2 wherein conductive members have anon-uniform current distribution therethrough and said plurality ofconductive bridging paths are so disposed as to provide substantiallyequal inductance over each parallel path.

4. The apparatus of claim 1 wherein said contacting means comprises aplurality of contacting elements adapted to engage said contact surfacesto form parallel conductive paths at points between each element andeach contact surface, and means for providing a geometry for each pathin relation to said separable conductive members such as to provide asubstantially equal inductance for the currents therethrough resultingfrom said pulse-source of electrical energy applied to said conductivemembers.

5. The apparatus of claim 4 wherein said contacting means furthercomprises force-distributing means adapted to receive a force appliedthereto, and pressure means responsive to said force-distributing meansfor providing hydrostatic-like pressure on said plurality of contactingelements, applying an equal pressure to each element so thatequalization of contact resistance is produced at each contact pointwhen said elements are in engagement with said contact surfaces.

6. The apparatus of claim 2 wherein each of said paths are defined froma respective point of contact on one conductive member to acorresponding point of contact on the other conductive member at each ofsaid contact surfaces, and said apparatus further comprises means forproviding successively longer path lengths as a function of distancealong said plane of separation toward said workspace.

7. The apparatus of claim 6 wherein said last mentioned means includessaid contact surfaces associated with each conductive member, saidcontact surfaces comprising raised conductive strips on opposite sidesof said plane of separation of said conductive members and positioned togenerally diverge toward said workspace.

8. The apparatus of claim 6 wherein said last mentioned means includessaid contact surfaces associated with each conductive member, saidcontact surfaces comprising depressions on opposite sides of said planeof separation of said conductive members and having contactable edgesgenerally diverging toward said workspace.

9. The apparatus of claim 6 wherein said last mentioned means includessaid contacting means having each successive conductive bridging path ofdifferent length, successively increasing with distance toward saidworkspace.

10. The apparatus of claim 9 wherein said contacting means includes amultitude of laminar blades having contacting edges adapted forengagement with said contact surfaces, a channel disposed between thecontacting edges of said blades, the depth of said channel increasingwith distance toward said workspace for successively increasing theinductance through each of said blades so that the inductance in each ofsaid current paths is equalized.

11. Apparatus for electromagnetically forming a workpiece, comprising apair of separable conductive dies having an open position for insertionand removal of the workpiece and a closed position defining a workspacefor the forming operation, said dies being generally planar and havingrelative movement for separation in the plane defined thereby, said dieshaving insulatively spaced interface surfaces defining the region ofseparation therebetween and contact surfaces on each side of said regionof separation generally parallel to the plane of movement, and acontactor movable relative to said contact surfaces at generally rightangles thereto for forming a connecting bridge across said region ofseparation on engagement with said contact surfaces when said dies arein said closed position, said contactor and said contact surfacespermitting any recoil movement generally parallel to the plane ofmovement of said conductive dies While maintaining said engagementduring the forming of the workpiece.

12. The apparatus of claim 11 wherein said contactor comprises amultitude of laminar blades for bridging said contact surfaces to form amultitude of parallel paths thereacross, the length of each successiveparallel path being such as to provide sufficiently varying inductancesto compensate for the non-uniform current distribution through the diesso as to provide a uniform reactance through each current path in thedies.

13. The apparatus of claim 12 wherein said contactor comprises ahydrostatic-like pressure distributing means, and said apparatusincludes force producing means for driving said contactor intoengagement with said contact surfaces and for maintaining a forcethereon sufficient to produce a uniform pressure at each contact pointthereby providing equal contact resistances thereat.

14. The apparatus of claim 13 comprising a further force producing meanscoupled to one of said dies for moving same into said open and closedposition, and control means coupled to both of the force producing meansfor sequentially moving said dies into said closed position for aforming operation, moving said contactor into contacting engagement,moving said contactor into disengagement after the forming operation,and then moving said dies into said open position,

References Cited UNITED STATES PATENTS 3,210,509 10/1965 Alf 72-4563,253,443 5/1966 Malmberg 7256 3,391,558 7/1968 Deeg 72-56 3,347,074'10/ 1967 Eilers et al. 7256 3,429,159 2/1969 Wildi 7256 3,430,4723/1969 Furth 7256 RICHARD J. HERBST, Primary Examiner UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3 Dated October 5,1971 Paul Wildi Inventor(s) It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

In the heading to the printed specification, lines 4 and 5, "GulfGeneral Atomic Incorporated, San Diego, Calif." should read Gulf OilCorporation, a corporation of Pennsylvania Signed and sealed this 9thday of May 1972.

(SEAL) Attest EDWARD M FLETCHER ,JR ROBERT GOTTSCHALK Attesting OfficerCommissioner of Patents OHM PC1-1050 (10-69) uscoMM-oc 60376-P69 U 5,GOVERNMENY PR NTNG OFFICE: 1969 O'IGQ-SSI

